Hello Rachel! Thank you for asking on HCM! I understand your concern, and would explain that your rattling sensation are just palpitations, that everyone has experienced on certain moments during his life. Do not worry about them. Returning to your question, I would say that generally palpitations are increased sensations when the person is on normal sinus rhythm. There is not any indirect way to confirm sinus rhythm, besides to register by means of a resting ECG during palpitations, or to undergo an ambulatory 24 to 48 hours ECG monitoring (hoping that palpitations will be present during registrations). So I would recommend you to perform an ambulatory ECG monitoring (Holter) to rule out any possible arrhythmic events (ectopic beats, supraventricular paroxysmal arrhythmia,etc), and some additional lab tests like complete blood count (to rule out anemia), thyroid hormone levels (for any possible dysfunction), fasting glucose, chest X ray, and if suspicions are raised a cardiac ultrasound. Hope to have been helpful! Greetings! Dr. Iliri